Optical inspection of laser vias

ABSTRACT

An automated optical inspection system including a source of electromagnetic radiation for delivering a radiation beam on an article to be inspected, a plurality of sensors arranged with respect to the radiation beam for sensing a plurality of radiation properties associated with the radiation beam impinging at least at a zone of impingement on a substance found on the article to be inspected, the plurality of sensors including a luminescence sensor for sensing luminescence of the substance due to the beam impinging thereon and a reflectance sensor for sensing reflectance of the beam from the substance the sensors transmitting information signals based on the radiation properties sensed by the sensors and a processor in communication with the sensors operative to receive the information signals for a plurality of zones of impingement, to combine the signals from the sensors and to analyze them, and to generate an output indicating the presence of defects based on the analysis.

FIELD OF THE INVENTION

[0001] The present invention relates generally to automated opticalinspection (AOI) systems and particularly to an AOI system forinspecting and detecting defects in laser-drilled vias in printedelectrical circuits.

BACKGROUND OF THE INVENTION

[0002] Most multi-layer printed circuit boards (“PCB”s) have vias, i.e.,passageways from one layer to another, which generally are plated toprovide electrical contact between the layers. Vias may be formed inmany ways, for example by means of apertures in the required x-ypositions in each layer, such that when the layers are joined togetherone on top of another and properly registered, the apertures define thevia path.

[0003] Recently vias have been made by first forming a laminatedmulti-layer board, and then by drilling the vias by means ofphotoablating and/or photo-cutting with a laser beam. Two examples ofwidely used lasers are frequency tripled (or quadrupled) pulsed YAGlasers (wavelength 355 or 266 nm) and CO₂ lasers (wavelength about 10.6μm). Both types of lasers can easily cut PCB laminate materials, such asglass-epoxy or polyimide. These two types of lasers have differentadvantages and disadvantages. For example, the laser beam of a YAG lasercuts through copper. This characteristic offers the advantage of beingable to use a YAG laser to prepare vias on substrates that are coatedwith copper, however one can overdrill the laminate (insulating layer)into the copper of the lower layer if precautions are not taken.Conversely, the laser beam of a CO₂ laser does not cut through thecopper, thus there is no danger of overdrilling. However a CO₂ laser cannot be used to prepare vias on substrates coated with copper.Consequently, when a CO₂ laser is used, metal must be removed from thetop layer where it is desired to drill a via, for example by etching,which does not have to be done for a YAG laser.

[0004] FIGS. 1A-1F illustrate different typical defects associated withlaser-drilled vias. The figures show an upper copper layer 2, a laminatelayer 3 and a lower copper pad 4, wherein it is desired to drill a via 5from upper layer 2 down to the top of pad 4. FIG. 1A illustrates anunderdrilled via, which of course means that although the via is platedwith copper, no electrical connection will be made between layer 2 andpad 4. FIG. 1B illustrates an overdrilled via, which means that the viais drilled through pad 4 resulting in too little metal being left on pad4 for a reliable electrical connection between layer 2 and pad 4. FIG.1C illustrates “throw out”, i.e., debris 6 from photoablation of thelayers being left in via 5, which can cause plating or electricalconnection problems. FIG. 1D illustrates the presence of foreignmaterials 7 in the via, which can cause plating or electrical connectionproblems. FIG. 1E illustrates an underplated via, namely a properlydrilled via having plating 8 that is not suitably deposited which canlead to an insufficient electrical connection. FIG. 1F illustrates via 5misregistered with pad 4, which, although not being a defect in thedrilling process per se, nevertheless is a defect which must be detectedbecause it too can lead to an insufficient electrical connection.

[0005] Although automated optical inspection (AOI) systems are typicallyused to inspect PCBs, nevertheless no AOI system is known which canaccurately, repeatably and reliably detect various defects inlaser-drilled vias, independently of whether or not the PCB underinspection, and the vias thereon, are cleaned prior to inspection.Moreover no laser drill repair station is known to inspect substantiallyall laser drill vias on a PCB and to automatically repair only thosedefective laser drill vias having defect types that are repairable.

[0006] U.S. Pat. No. 5,216,479 shows and describes an optical inspectionsystem for inspecting a surface of a laminate operative to distinguishbetween a first material, such as a printed circuit board laminate, anda second material, such as copper formed thereon, and employing a laserilluminator selectively illuminating the surface and signal analyzersoperative to sense and analyze fluorescent light and reflected lightresulting from illumination by the laser.

SUMMARY OF THE INVENTION

[0007] The present invention seeks to provide a novel AOI system whichcan accurately, repeatably and reliably detect and distinguish variousdifferent defects in laser-drilled vias. The present invention cansimultaneously inspect through holes and laser-drilled vias. Preferablythe detection of the various different defects can be made independentlyof whether or not the PCB under inspection, and the vias thereon, arecleaned prior to inspection.

[0008] Additionally, the present invention seeks to provide a novel AOIsystem which can accurately, repeatably and reliably detect anddistinguish various different defects in laser-drilled vias, and whichcan automatically repair, for example by redrilling, those defectivevias which are repairable. Preferably, if non-repairable defects aredetected then no vias, such as vias having repairable defects, areredrilled.

[0009] The present invention uses a combination of inputs from at leasttwo optical data channels which sense one or more of three differentparameters of a radiation beam impinging on substances found on the PCB:luminescence of the substance (laminate, copper layer, copper pad,debris, etc.) due to the beam impinging thereon, reflection of the beamfrom the substance, and transmission of the beam at the point ofimpingement. Each data channel preferably is adjustable independently ofthe other channels for optimal performance. Although most preferably thebeam is a laser beam, nevertheless the invention can be carried out withany coherent or non-coherent monochromatic or polychromatic light beam,or any other radiation, electromagnetic wave or acoustic beam, forexample.

[0010] It is noted that the term “luminescence” refers to the emissionof visible or non-visible electromagnetic radiation as a result ofabsorption of exciting energy in the form of photons, charged particles,or chemical change. The term luminescence includes both fluorescence andphosphorescence. In “fluorescence”, an atom or molecule emits detectableradiation in passing from a higher to a lower electron excitation state.The term fluorescence relates to phenomena in which the time intervalbetween absorption and emission of energy is extremely short, typicallyin the range of 0.01-1000 microseconds. The term “phosphorescence”relates to the emission of radiation continuing after excitation hasceased, and may last from a fraction of a second to an hour or more.

[0011] The fluorescence of metallic conductors on PCBs, such as copper,under short wavelength visible light (for example 442 nm laser lightemitted by a helium cadmium CW laser) is measurably less, generally byan order of magnitude, than the fluorescence of typical PCB laminatematerials, such as glass-epoxy or polyamide. In addition, copperreflects light much better than such typical PCB laminate materials. Thepresent invention exploits the large differences in fluorescence andreflectance of laminate compared to conductor in order to distinguishbetween portions of the via which are laminate and portions which arecopper.

[0012] The reflectance and luminescence sensors preferably are placedabove a horizontal PCB to be inspected, and are angled with respect tothe via. The angled orientation of the sensors permits them to view andto provide sensed information along the entire depth of the via. Bysimultaneously combining and analyzing sensor inputs from at least twochannels, the AOI system can detect and distinguish between at some ofthe various defects shown in FIGS. 1A-1F. The combined information candistinguish between defects in the via as opposed to defects on theupper surface of the PCB or at the bottom of the via. Most importantly,the combined information can distinguish between underdrilling orresidue debris which can be repaired by further laser drilling, andother defects such as via hole misalignment that generally can not bereadily repaired. Preferably the sensor inputs are signals from thecombination of two of the luminescent, reflective and transmissivesensors respectively. Alternatively, the sensor inputs may be two signalinputs from the luminescent sensor, or two inputs from the reflectivesensor, wherein each input is interpreted with reference to one ofvarious thresholds of luminescence or reflectance, and then combined todetect the presence of defects.

[0013] The transmission sensor, simultaneously with the reflectance andluminescence sensors, can sense light that passes through the hole fromone side of the PCB to another, thereby providing information regardingthe position, and possible defects, of through holes. The sensitivity ofthe system can be adjusted as desired, in order to distinguish betweendefects which are sufficiently small in size so as not to pose anyproblem in plating or electrical conductivity, as opposed to thosedefects which are of a size sufficient to pose a problem. For example,by adjusting the sensitivity of the system, the system can distinguishbetween debris remaining in a via which may hinder plating or electricalconductivity, for example debris which is 3-4 μm size, as opposed todebris which is not considered a hindrance to plating or electricalconductivity, for example debris of only 1 μm size.

[0014] The system can also be used to scan a PCB before or aftercleaning the PCB with a cleaning agent, or before or after plating.Preferably, when the system is used to inspect a PCB prior to cleaning,only one input is used, for example from the luminescence sensor,however the signal from the one sensor is analyzed with respect to twodifferent thresholds and then combined to determine the presence ofdefects.

[0015] Additionally, the system can be used to inspect substantially allthe vias on a region of a PCB and automatically distinguish betweenrepairable and not repairable vias in the inspected region. Those viaswhich are deemed repairable are subsequently repaired. Preferably,repairable and not repairable vias are distinguished as a function ofone or more of the type of defect and the location of the defective via.Thus, for example, underdrilled vias may be deemed repairable and thusmay be subsequently automatically further drilled so that adequateelectrical contact can be made with the affected via. Preferably, thesystem includes an intelligent decision tree so that if a PCB includes anon-repairable via, for example an overdrilled or misaligned via, noneof the repairable vias on the PCB are automatically repaired in order toconserve repair resources.

[0016] There is thus provided in accordance with a preferred embodimentof the present invention an automated optical inspection systemincluding an automated optical inspection system including a source ofelectromagnetic radiation for delivering a radiation beam on an articleto be inspected;

[0017] a plurality of sensors arranged with respect to the radiationbeam for sensing a plurality of radiation properties associated with theradiation beam impinging at least at a zone of impingement on asubstance found on the article to be inspected, wherein the plurality ofsensors includes a luminescence sensor for sensing luminescence of thesubstance due to the beam impinging thereon and a reflectance sensor forsensing reflectance of the beam from the substance and wherein thesensors transmit information signals based on the radiation propertiessensed by said sensors; and

[0018] a processor in communication with said sensors operative toreceive the information signals for a plurality of zones of impingement,to combine said signals from the sensors and to analyze them, and togenerate an output indicating the presence of defects based on saidanalysis.

[0019] Preferably, a preferred embodiment of the system includes atleast one or more of the following:

[0020] The defects include defects that are automatically repairable anddefects that are not automatically repairable.

[0021] The luminescence sensor is a fluorescence sensor.

[0022] The article to be inspected is PCB with a via formed which has adepth, and the reflectance and luminescence sensors are positioned at anangle with respect to the via, such that said sensors can view andprovide sensed information generally along the entire depth of said via.

[0023] The sensors have an adjustable sensitivity.

[0024] The sensitivity of each sensor is adjustable independently of theother.

[0025] The position of each sensor is adjustable independently of theother.

[0026] The radiation beam is a laser beam.

[0027] The processor comprises a filter to filter out a level ofluminescence which could cause a false alarm.

[0028] The processor includes a filter to filter out a level ofreflectance which could cause a false alarm.

[0029] The processor processes the information signals into binarysignals with reference to predetermined detection thresholds forluminescence and reflectance.

[0030] The processor generates a binary image for each of luminescenceand reflectance signals.

[0031] The processor multiplies the binary images together, andcalculates a composite luminescence and reflectance image.

[0032] The processor compares the composite images to predetermineddefect parameters, and produces a defect report.

[0033] The system includes a drilling laser unit operative to drill ahole or via in a PCB; the automated optical inspection system and saiddrilling laser are in electrical communication with a controller; and aposition of the hole or via is fed from the automated optical inspectionsystem to the controller, and the controller instructs the drillinglaser to drill the hole or via.

[0034] The position of the hole or via is fed from the automated opticalinspection unit if said hole or via is analyzed by the processor to bedefective and repairable.

[0035] The drilling laser is operative to avoid drilling any holes orvias on said PCB if any said hole or via is determined by the automatedoptical inspection system to be defective and not repairable.

[0036] The drilling laser comprises a CO₂ laser.

[0037] The controller is also the processor.

[0038] The drilling laser is said source of electromagnetic radiationfor delivering a radiation beam on an article to be inspected.

[0039] There is thus provided in accordance with a preferred embodimentof the present invention an automated optical inspection systemincluding:

[0040] a source of electromagnetic radiation for delivering a radiationbeam onto an article to be inspected;

[0041] a sensor arranged with respect to the radiation beam for sensinga radiation property associated with said radiation beam impinging atleast at a zone of impingement on a substance found on the article to beinspected, wherein the sensor transmits information signals based on theradiation properties sensed by said sensor; and

[0042] a processor in communication with said sensor, the processorbeing operative to:

[0043] receive information signals for a plurality of zones ofimpingement,

[0044] extract from the information signal additional information aboutsaid article by analysis of the information signals with reference to atleast two different thresholds; and

[0045] generate an output indicating the presence of a defects based onanalysis of the extracted information.

[0046] Preferred embodiments of the invention include one or more of thefollowing:

[0047] The processor further includes an information combiner operativeto combine additional information about said article obtained byanalysis of the information signals with reference to the at least twodifferent thresholds.

[0048] The detected defects include defects that are classified asautomatically repairable and defects that classified as being notautomatically repairable.

[0049] The sensor is a luminescence sensor operative to sensefluorescence.

[0050] The article to be inspected is a PCB with a via formed therein,wherein the via has a depth, and wherein the luminescence sensor ispositioned at an angle with respect to the via, such that it can viewand provide sensed luminescence information generally along the entiredepth of said via.

[0051] The sensor has an adjustable sensitivity.

[0052] The radiation beam is a laser beam.

[0053] The processor includes a filter to filter out a level ofluminescence which could cause a false alarm.

[0054] The processor processes the information signals to produce a setof binary images with reference to at least two different predetermineddetection thresholds for luminescence.

[0055] The processor multiplies the binary images together, andcalculates therefrom a composite image.

[0056] The processor compares the composite image to predetermineddefect parameters, and produces a defect report based on the comparison.

[0057] The system further includes a drilling laser operative to drill ahole or via in a PCB; automated optical inspection system and thedrilling laser are in electrical communication with a controller, and aposition of the hole or via is fed from said automated opticalinspection system to the controller, which instructs said drilling laserto drill the hole or via.

[0058] The position of the hole or via is fed from said automatedoptical inspection device if said hole or via is analyzed by theprocessor to be defective and repairable.

[0059] The drilling laser is operative to avoid drilling holes or viason said PCB if upon inspection a hole or via on the PCB is determined bythe automated optical inspection system to be defective and notrepairable.

[0060] The laser comprises a CO₂ laser.

[0061] The controller is said processor.

[0062] The drilling laser is the source of electromagnetic radiation fordelivering a radiation beam on an article to be inspected.

[0063] There is thus provided in accordance with a preferred embodimentof the present invention, a system for repairing defective laser drilledholes in an electrical circuit to be inspected including:

[0064] an automated optical inspection subsystem operative to inspect aPCB and to provide output indications of defective and non-defectivevias on the PCB, and

[0065] a controller in communication with the automated opticalinspection system and with a laser drill, wherein the controller isoperative to instruct the laser drill to automatically redrill at leastsome holes on the PCB indicated as being defective.

[0066] The output indication of repairable and non-repairable holesfurther indicates which defective holes are repairable, and the laserdrill automatically redrills defective and repairable holes.

[0067] The laser drill avoids drilling any holes if the automatedoptical inspection system detects a defective and non-repairable hole.

[0068] The laser drill is a CO₂ laser drill.

[0069] The laser is a YAG laser drill, and the automated opticalinspection system determines a characteristic of repairable defectiveholes.

[0070] The characteristic of a repairable defective hole is the size ofan artifact in the hole.

[0071] The characteristic of a repairable defective hole is thethickness of a residue laminate in the hole.

[0072] The laser drill is operative to provide an amount of energyadapted to clear the hole without overdrilling the hole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The present invention will be understood and appreciated morefully from the following detailed description, taken in conjunction withthe drawings in which:

[0074] FIGS. 1A-1F are six simplified sectional illustrations ofdifferent defects associated with laser-drilled vias of the prior art;

[0075]FIG. 2 is a simplified block diagram illustration of an automatedoptical inspection system constructed and operative in accordance with apreferred embodiment of the present invention;

[0076]FIG. 3 is a simplified flow chart of the system of FIG. 2;

[0077]FIG. 4A is simplified sectional illustration of a defectless via;

[0078]FIG. 4B is a simplified illustration of graphs of fluorescence andreflectance associated with the via of FIG. 4A;

[0079]FIG. 4C is a simplified illustration of binary imagescorresponding to the fluorescence and reflectance associated with thevia of FIG. 4A, and a combined image of the binary images;

[0080]FIG. 5A is simplified sectional illustration of a via with anartifact;

[0081]FIG. 5B is a simplified illustration of graphs of fluorescence andreflectance associated with the via of FIG. 5A;

[0082]FIG. 5C is a simplified illustration of binary imagescorresponding to the fluorescence and reflectance associated with thevia of FIG. 5A, and a combined image of the binary images;

[0083]FIG. 6A is simplified sectional illustration of a via with firstunderdrilled hole;

[0084]FIG. 6B is a simplified illustration of graphs of fluorescence andreflectance associated with the via of FIG. 6A;

[0085]FIG. 6C is a simplified illustration of binary imagescorresponding to the fluorescence and reflectance associated with thevia of FIG. 6A, and a combined image of the binary images;

[0086]FIG. 7A is simplified sectional illustration of a via with asecond underdrilled hole, shallower than the underdrilled hole of FIG.6A;

[0087]FIG. 7B is a simplified illustration of graphs of fluorescence andreflectance associated with the via of FIG. 7A;

[0088]FIG. 7C is a simplified illustration of binary imagescorresponding to the fluorescence and reflectance associated with thevia of FIG. 7A, and a combined image of the binary images;

[0089]FIG. 8A is simplified sectional illustration of a via with anoverdrilled hole;

[0090]FIG. 8B is a simplified illustration of graphs of fluorescence andreflectance associated with the via of FIG. 8A;

[0091]FIG. 8C is a simplified illustration of binary imagescorresponding to the fluorescence and reflectance associated with thevia of FIG. 5A, and a combined image of the binary images;

[0092]FIG. 9A is simplified sectional illustration of a misregisteredvia;

[0093]FIG. 9B is a simplified illustration of graphs of fluorescence andreflectance associated with the via of FIG. 9A;

[0094]FIG. 9C is a simplified illustration of binary imagescorresponding to the fluorescence and reflectance associated with thevia of FIG. 9A, and a combined image of the binary images;

[0095]FIG. 10 is a simplified illustration of a via on a PCB beforecleaning the PCB with a cleaning solution;

[0096]FIG. 11 is a simplified flow chart showing another preferred modeof operation of the system of FIG. 2;

[0097]FIG. 12 is a simplified illustration of a graphs of fluorescenceof the via shown with reference to a double threshold; and

[0098]FIG. 13 is a simplified illustration of an automated opticalinspection and PCB laser drilling system, constructed and operative inaccordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0099] Reference is now made to FIG. 2 which illustrates an automatedoptical inspection system 10 constructed and operative in accordancewith a preferred embodiment of the present invention.

[0100] System 10 preferably includes a source 12 of electromagneticradiation for delivering a radiation beam 14 to an article to beinspected. A preferred radiation source is a laser, such as a 10 mWhelium-cadmium CW laser available from Liconix of California, U.S.A.,but it is appreciated that the present invention encompasses any kind ofsuitable laser or radiation source. A typical article to be inspected isa suitable electrical circuit, such as a PCB 16 with a via 18 formedtherein. Via 18 may be a via having any arbitrary depth to reach somepredetermined inner layer in a multi-layered PCB 16, or a through holepassing all the way through PCB 16. Via 18 may be formed by mechanicaldrilling, by drilling using a suitable laser drill such as a CO₂, YAG oreximer laser, by etching or by any other suitable via hole generationprocess.

[0101] A plurality of sensors are preferably arranged with respect toradiation beam 14 for sensing a plurality of radiation propertiesassociated with radiation beam 14 impinging at a zone of impingement 20(shown as a phantom-line circle in FIG. 2) on a substance found on thearticle to be inspected. The “substance” can be the wall of the via 18,an artifact found in the via, a defect in the via, extraneous matter,solvents, etc. The plurality of sensors preferably includes aluminescence sensor 22 for sensing luminescence, such as fluorescence orphosphorescence, of the substance due to beam 14 impinging thereon, areflectance sensor 24 for sensing reflectance of beam 14 from thesubstance, and a transmission sensor 26 for sensing transmission of beam14 at the zone of impingement 20. The sensors 22, 24 and 26 transmitinformation signals based on the radiation properties sensed by sensors22, 24 and 26 to a processor 28 that processes the signals for each zoneof impingement of beam 14. A scanner (not shown) may be used to passbeam 14 over the entire area and depth of via 18, for example in asequence of swaths or other suitable systematic pattern.

[0102] Each sensor 22, 24 and 26 preferably has an adjustablesensitivity, and the position and/or sensitivity and/or threshold ofdetectivity of each sensor can be adjusted independently of the other.In this manner, the performance of system 10 can be adjusted andoptimized as required. Additionally, as will be described in greaterdetail hereinbelow, a signal from either luminescence sensor 22 orreflectance sensor 24 respectively may be simultaneously processed withreference to separate thresholds to extract additional information fromthe signal, and subsequently the additional information is combined inorder to detect various different defects that would not be detectableby using a single signal from any one of luminescence sensor 22,reflectance sensor 24 and transmission sensor 26, or by combining anyplurality of signals from one or more of the sensors 22, 24 and 26.Reflectance and luminescence sensors 22 and 24 are preferably positionedat an angle with respect to via 18, such that sensors 22 and 24 can viewand provide sensed information generally along the entire depth of via18.

[0103] A preferred luminescence sensor 22 is a photo sensor, preferablya photo diode or photomultiplier type sensor operative to sensefluorescence/phosphorescent emission, although other types of sensorsmay be employed depending upon the article being inspected and theenergy level and/or quantity of radiation to be sensed.

[0104] Reference is now made to FIG. 3 which is a simplified flow chartof system 10 illustrating operation thereof in accordance with apreferred embodiment of the present invention. Luminescence sensor 22provides information related to the luminescent intensity of lightemissions resulting from beam 14 impinging on zone 20 and thisinformation is fed to a luminescent intensity channel 30 of processor28. Similarly, reflectance sensor 24 provides information related to thereflective intensity of light from beam 14 being reflected from zone 20and this information is fed to a reflective intensity channel 32 ofprocessor 28.

[0105] Luminescent intensity channel 30 preferably is provided with oneor more filters 34 that filter out spurious appearances of luminescencetypically associated with false alarm defects, such as islands, pads,etc. Similarly, reflective intensity channel 32 is preferably providedwith one or more filters 36 that filter out spurious appearances ofreflectance typically associated with false alarm defects, such as thoseassociated with brightness or tolerable sizes of particles, such asdust, for example. Filters 34 and 36 may be optical filters or aprocessor (not shown) applying suitable algorithms, for example.Appropriate filtering parameters and sensitivity may be pre-set,manually adjustable or programmable, as desired.

[0106] The outputs of channels 30 and 32 as filtered by filters 34 and36, respectively, are processed by processor 28 into binary signals withreference to predetermined detection thresholds for luminescence andreflectance respectively. A binary image is generated for each channel30 and 32, and these binary images are combined, preferably bymultiplying them together, pixel by pixel. In this manner, processor 28calculates a composite luminescence and reflectance channel image 38.

[0107] The composite image 38 is then measured and analyzed withreference to a predetermined defect parameters 40. For example, typicaldefect parameters include a net pad size or a particle size threshold. Atypical particle size threshold would be a particle size of 1 μm,because such a size is not considered a hindrance to plating orelectrical conductivity. Based on these defect parameters 40 and thecomposite images 38, a defect report 42 is produced, which may bedisplayed or printed, for example.

[0108] Reference is now made to FIGS. 4A, 4B and 4C which pictoriallyillustrate how the luminescence and reflectance signals are combined, asdescribed hereinabove with reference to FIG. 3, to detect defects. FIG.4A illustrates a defectless via 50 with an upper copper layer 52 and alower copper pad 54, separated by a laminate 56. Beam 14 (FIG. 2) scansthe entire depth and area of via 50. For each scan pass of beam 14 overa via 50, as seen in FIG. 4B, a luminescence intensity in the exampleshown, relating to fluorescence and designated graph F, and areflectance intensity, designated graph R, are sensed. It is noted thata via 50 preferably is sensed in multiple passes of scan beam 14.Additionally it is seen in graph F that for a fluorescence sensor, thefluorescence of the copper layer 52 and pad 54 is relatively low,whereas the fluorescence of the laminate 56 forming walls 57 of via 50is relatively high. Thus the fluorescence of laminate 56 appears as twopeaks in the fluorescence graph F of FIG. 4B. The peaks are above apredetermined fluorescence threshold FT, which means that processor 28recognizes them as peaks associated with a non-metal material.

[0109] Conversely, as seen in graph R of FIG. 4B the reflectance of thecopper layer 52 is relatively high, whereas the reflectance of thelaminate 56 is relatively low. Typically, the reflectance of copperlayer 52 is higher than the reflectance of pad 54 because pad 54 is moredistant from reflectance sensor 24 (FIG. 2). Preferably a predeterminedreflectance threshold RT is set intermediate of typical reflectancelevels of copper layer 52 and pad 54 so as to define the circumferenceboundary of via 50. Thus the reflectance of laminate 56 appears as tworeverse peaks in the reflectance graph R of FIG. 4B. Inasmuch asreflectance of the copper layer 52 is above threshold RT, while thereflectances of pad 54 and laminate 56 are below that threshold,processor 28 can readily distinguish between them to spatially definethe circumference of via 50.

[0110] In FIG. 4C, it is seen that a binary image of all of subsequentscanning passes of the fluorescence sensor is generated. The binaryimage is taken with respect to thresholds FT and RT and includes acentral, shaded circular region 58 inside a clear, circular ring 60,which is in turn bounded by a shaded region 62. The clear ring 60corresponds to the part of the signal represented in graph F and shownas fluorescence peaks associated with the laminate walls of the via 50which are above threshold FT, whereas regions 58 and 62 correspond tofluorescence signal in graph F for pad 54 and layer 52, respectively.Conversely, a binary image of all of the scanning passes of thereflectance sensor is generated. The binary image includes a circularregion 64 corresponding to the reflectance of pad 54 and laminate 56,both of which are below reflectance threshold RT, which is bounded by aclear region 66 which corresponds to the reflectance of pad 52 and isabove threshold RT. Thus, as seen, circular region 64 defines thespatial region of via 50.

[0111] In accordance with a preferred embodiment of the presentinvention, each of the shaded regions 58, 62 and 64 shown in FIG. 4C areassigned a value of 1, while each of the clear regions 60 and 66 areassigned a value of 0. Processor 28 multiplies these values together toform a composite image 70, shown in FIG. 4C, which indicates the spatialregion inside via 50 which are suitable for electrical contact. Thuscomposite image 70, shown in FIG. 4C, is seen to represent a defectlessvia 50 in which the entire spatial region inside via 50 is suitable forelectrical contact.

[0112] Reference is now made to FIGS. 5A, SB and SC which pictoriallyillustrate how the luminescence and reflectance signals are combined todetect a defect due to the presence of an artifact that partially coverspad 54. FIG. 5A illustrates via 50 with an artifact 72, such as debrisleft over from an etching process, on lower copper pad 54. Thefluorescence of laminate 56 forming walls 57 still appears as twoprincipal peaks in the fluorescence graph F of FIG. 5B, but there is anadditional peak associated with artifact 72. As seen, some part of eachof the peaks, including the peak associated with artifact 72, extendsabove a predetermined fluorescence threshold FT, which means thatprocessor 28 recognizes these peaks as being associated with a non-metalmaterial.

[0113] Conversely, as seen in graph R of FIG. 5B, the reflectance of thecopper layer 52 is relatively high, whereas the reflectance of pad 54,laminate 56, artifact 72 each are below the reflectance threshold RT.Note that the reflectance of artifact 72 is different than that of pad54 and of laminate 56, however in the example shown each of therespective intensities of reflectance is less than reflectance thresholdRT.

[0114] In FIG. 5C, it is seen that the binary images of the fluorescenceand reflectance channels, taken with respect to thresholds FT and RT,are combined in the manner described with respect to FIG. 4C hereinaboveto form a composite image 74 corresponding to composite image 70 in FIG.4C. It is seen that anomaly 76 corresponds to artifact 72 (FIG. 5A),namely a non-metal fluorescent body that is located in a region thatshould be completely occupied by copper pad 54. Depending on the size ofanomaly, via 50 may be classified as defective or non-defective inaccordance with inspection parameters.

[0115] Reference is now made to FIGS. 6A, 6B and 6C and to FIGS. 7A, 7Band 7C which pictorially illustrate how the luminescence and reflectancesignals are combined to detect a defect due to an underdrilled hole, itbeing noted that sometimes a thin layer of residue laminate may notnecessarily render a via defective, while conversely a thicker layer orresidue laminate may result in a defect. FIGS. 6A, 6B and 6C illustratea partially underdrilled hole which is not defective while FIGS. 7A, 7Band 7C illustrate an underdrilled hole having a thicker residue laminatethat is defective.

[0116]FIG. 6A illustrates a first underdrilled via hole 78 having anunderdrilled region 79 thereinside. Although via 78 is underdrilled itis not defective. As seen in FIG. 6B, the fluorescence intensity oflaminate 56 received from the walls 57 still appears as two peaks in thefluorescence graph F, and the fluorescence of underdrilled hole 78 isseen to be different than that of via 50 as shown in FIG. 4B. It isnoted that the fluorescence intensity between the peaks in graph F ofFIG. 6B, corresponding to underdrilled region 79 is higher than graph Fof FIG. 4B. This is because in underdrilled via hole 78 a thin layer ofresidue due to underdrilling is present in underdrilled region 79 whichtypically results in a small but measurable luminescent intensity.Furthermore, it is seen that despite the presence of luminescence, theintensity of graph F of FIG. 6B does not exceed fluorescence intensitythreshold FT, thus indicating that pad 54 in FIG. 6A laminate residue 79is not so thick as to prevent good electrical contact with pad 54.

[0117] Conversely, the reflectance of copper layer 52 in FIG. 6A isrelatively high, whereas the reflectance of laminate 56 forming walls 57and pad 54 in underdrilled via hole 78 are relatively low. Note thatalthough the reflectance graph R of underdrilled via hole 78 isdifferent than reflectance graph R of defectless via 50 (FIG. 4A), thereflectance graph R corresponding to pad 54 of underdrilled hole 78likewise does not exceed threshold RT in FIG. 6B.

[0118] In FIG. 6C, it is seen that binary images of the fluorescence andreflectance channels, taken with respect to thresholds FT and RT, arecombined to form a composite image 80 which is substantially similar tocomposite image 70 for defectless via 50. It is noted that although aresidue is present, suitable electrical contact with a pad 54 may stillbe made. Thus because the luminescence is below threshold FT no defectis detected.

[0119] Reference is now made to FIGS. 7A, 7B and 7C which pictoriallyillustrate how the luminescence and reflectance signals are combined todetect a defect due to another underdrilled hole which has a quantity ofresidue that renders the underdrilled hole defective. FIG. 7Aillustrates an underdrilled via hole 84, underdrilled via hole 84 beingshallower, namely it contains a greater quantity of residue inunderdrilled region 85, as compared to underdrilled via hole 78 of FIG.6A. As seen in graph F of FIG. 7B the fluorescence of laminate 56forming walls 57 still appears as two peaks, but the fluorescence of theregion 85 inside underdrilled via hole 84 is seen to be different thanthat of defectless via 50, as shown in FIG. 4B, and different than thatof underdrilled hole 78, as shown in FIG. 6B. It is noted that thefluorescence intensity between the peaks in graph F of FIG. 7B is higherthan graph F of FIG. 4B and graph F of FIG. 6B. This is because inunderdrilled via hole 84 a relatively thick layer of residue is presentin underdrilled region 85, which typically results in a relatively largemeasurable luminescent intensity. Furthermore, it is seen that theluminescent intensity graph F of FIG. 7B exceeds fluorescence intensitythreshold FT, thus indicating a defect because suitable electricalcontact can not be made with pad 54 in FIG. 7A.

[0120] In FIG. 7C, it is seen that binary images of the fluorescence andreflectance channels, taken with respect to thresholds FT and RT, arecombined to form a composite image 90. Because fluorescent graph F inFIG. 7B exceeds threshold FT, it is seen in FIG. 7C that there is only aclear region 92 and shaded region 58 (FIG. 4C) is absent. Thus uponmultiplication with circular region 64 in FIG. 7C, which defines thespatial region of underdrilled via hole 84 received from graph R, a nullresult is obtained, as shown by the phantom lines of composite image 90which indicate where the pad should have been located. Thus it isindicated that pad 54 is entirely covered and suitable electricalcontact therewith can not be made.

[0121] It is thus appreciated from FIGS. 6B, 6C and 7B and 7C thatprocessor 28 (FIG. 2) can distinguish between different depths ofunderdrilled holes. Moreover, by choosing appropriate thresholds FT andRT, the sensitivity of a via to the presence of underdrilling residuemay be determined. Thus for example, a first threshold may be applied tovarious vias that require a very high level of cleanliness, whileanother threshold may be applied to vias where a larger quantity ofresidue is still acceptable without rendering the via defective. Suchthresholds may be applied for example as a function of physical locationin an electrical circuit, or as a function of a type or intended use.Additionally, multiple thresholds (not shown) may be provided to thesame via such that a first threshold is used to ascertain the presenceof a residue while a second and additional thresholds may be provided todetermining the quantity of residue in the via. Such a multiplethreshold arrangement may be beneficial, for example, in deciding firstwhether or not to redrill or clean out an underdrilled via 78, andadditionally to determine the amount of laser energy that needs to beapplied to clean out the via, for example if a YAG laser is used, inorder to ensure that redrilling does not damage the via by overdrilling.

[0122] Reference is now made to FIGS. 8A, 8B and 8C which pictoriallyillustrate how the luminescence and reflectance signals are combined todetect a defect due to an overdrilled via hole. FIG. 8A illustrates anoverdrilled via hole 100, i.e., a via hole having a break 102 in pad 54.As seen in FIG. 8B, the fluorescence intensity of laminate 56 in walls57 of overdrilled via hole 100 still appears as two peaks in thefluorescence graph F, however fluorescence graph F of overdrilled hole100 also includes a spike 104 representative of break 102 intermediateof the peaks representing laminate 56.

[0123] Conversely, as seen in graph R of FIG. 8B, the reflectance ofcopper layer 52 is above the reflectance threshold RT while thereflectance of sections of pad 54 surrounding break 102, althoughrelatively high, are less than reflectance threshold RT. The reflectanceof laminate 56 forming walls 57 and laminate 56 underneath break 102 arealso relatively low and less than the reflectance threshold RT. In FIG.8C, it is seen that the binary images of the fluorescence andreflectance channels, taken with respect to thresholds FT and RT, arecombined as described with respect to FIG. 4C to form a composite image106 which has an anomaly 108 corresponding to break 102 in overdrilledhole 100.

[0124] It is noted that the composite image 106 of FIG. 8C representingan overdrilled hole is very similar to image 74 (FIG. 5C) showing ananomaly 76 that corresponds to an artifact 72 (FIG. 5A). In accordancewith a preferred embodiment of the invention the distinction between aresidue artifact and an overdrilled hole is made respective of the typeof drilling process used to prepare the laser via. Thus for example, ifthe laser via was initially drilled using a CO₂ laser, which does notdrill through copper, the anomaly is assumed to be an artifact 76.However, if the laser via was drilled using a YAG laser, which is ableto drill through copper, the anomaly is assumed to be an overdrilledhole.

[0125] Reference is now made to FIGS. 9A, 9B and 9C which pictoriallyillustrate how the luminescence and reflectance signals are combined todetect a defect due to a misregistered hole. FIG. 9A illustrates viahole 110 misaligned with pad 54.

[0126] As seen in graph F of FIG. 9B, the fluorescence of laminate 56appears as one peak associated with the right-hand laminate wall 112that extends down to pad 54, and a broad band of relatively highfluorescence associated with the left hand wall 114 and a pad-less areaof laminate 56 at the bottom of via hole 110.

[0127] Conversely, as seen in graph R of FIG. 9B the reflectance ofcopper layer 52 and is relatively high and is above threshold RT. Thereflectance of laminate 56 appears as one reverse peak associated withthe laminate wall 112 that goes down to pad 54, and a broad band ofrelatively low reflectance associated with the wall 114 and pad-lessarea of laminate at the bottom of via 50. The reflectance of pad 54 isrelatively high compared to the reflectance of laminate 56, however itremains below threshold RT. In FIG. 9C, it is seen that the binaryimages of the fluorescence and reflectance channels, taken with respectto thresholds FT and RT, are combined to form a composite image 116which due to misregistration between via hole 110 and pad 54 ismisshaped, not round in the example shown, and small compared to aproperly formed via hole, for example via 50 in FIGS. 4A-4C.

[0128] While the above discussion has been with respect to a binarycomposition of signals from the input channels, it is appreciated bypersons skilled in the art that in order to further distinguish betweendifferent forms of defects various multiple thresholds or robustalgorithms operative to analyze the analogue signal may be provided.

[0129] The present invention can be used to scan a PCB both before andafter cleaning the PCB with a liquid cleaning solution. FIGS. 4A-9Cillustrate inspecting the via 50 generally after cleaning the PCB with aliquid cleaning solution. The cleaning solution removes most of thedebris left in the via and prepares the surface of copper layer 52 to befree of smudges and other artifacts that may affect reflectance orfluorescence. Typically when the PCB is cleaned before inspection thereis a pronounced difference between the fluorescence of the copper pad 54at the bottom of the via 50 and that of the laminate 56 which makes upthe walls 57 of the via 50. There is also a large difference in therespective reflectances of copper layers 52 and pads 54 located at thebottom of the various vias.

[0130] Reference is now made to FIG. 10 which is a simplifiedillustration of a via on a PCB prior to cleaning the PCB with a cleaningsolution, and to FIG. 11 which is a simplified flow chart showinganother preferred mode of operation of the system of FIG. 2 in which aPCB is inspected prior to cleaning.

[0131] Referring to FIG. 10, it is seen that before cleaning the PCBwith a cleaning solution, there may be at least some debris in a via 120and its surroundings. Specifically, there is typically a thin laminatelayer 122 at least partially covering a bottom pad 124 of via 120,and/or laminate material 126 or other non reflective debris may bedeposited on an upper copper layer 128 near via 120, such as materialthrown out during photoablation, fingerprint residue, oxidation and thelike. Such debris generally reduces reflectance of the copper.Additionally, if the reflectance threshold is reduced to accommodate thereduced reflectance undesired shiny spots may appear on bottom pad 124,for example where thin laminate layer 122 does not cover the entire pad124. It is thus appreciated that in such situations before cleaning,changes in the reflectance of the bottom pad 124 caused by thin laminatelayer 122 and unevenness in reflectivity of the upper copper layer 128may cause the reflective intensity channel 32 to provide irregularinformation or information that is significantly different from theinformation that would be provided after cleaning. These irregularitiestypically make it difficult to define the spatial boundaries of via 120or to detect the presence of defects inside via 120.

[0132] In a preferred embodiment of the present invention, forinspection of PCBs before cleaning, the reflective intensity channel 32is not used at all. Rather, the luminescent intensity signal for anon-defective via 120 is modeled and a signal (preferably fluorescence)from one of sensors 22 or 24 (FIG. 2) for each via 120 to be inspectedpreferably is analyzed with respect to two thresholds.

[0133] Referring now to FIG. 11, luminescence sensor 22 providesinformation related to the luminescent intensity of light emissionsresulting from beam 14 impinging on zone 20 (FIG. 2) and thisinformation is fed to a luminescent intensity channel 130 of processor28.

[0134] Luminescent intensity channel signal 130 is preferably treatedwith one or more filters 134 that filter out spurious appearances ofluminescence typically associated with false alarm defects, such asislands, pads, etc. Filter 134 may be an optical filters or suitablealgorithm, for example. Appropriate filtering parameters and sensitivitymay be pre-set, manually adjustable or programmable, as desired.

[0135] The outputs of channel signal 130 as filtered by filter 134 isprocessed by processor 28 into binary signals with reference to twopredetermined detection thresholds, namely an upper threshold and alower thereshold, as shown and described hereinbelow with respect toFIG. 12, to produce a first binary image respective of the upperthreshold 136 and a second binary image respective the lower threshold138. The first and second binary images for the upper and lowerthresholds respectively are multiplied together, pixel by pixel, in thesame manner as shown and described hereinabove, for example withreference to FIG. 4C. In this manner, processor 28 (FIG. 2) calculates acomposite image 140.

[0136] The composite image 140 is then measured and compared topredetermined defect parameters 142. For example, one kind of defectparameter may be a minimum pad size or a particle size threshold. Basedon these defect parameters 142 and the composite images 140, a defectreport 144 is produced, which may be displayed or printed, for example.

[0137] Reference is now made to FIG. 12 wherein graph A is a graph offluorescence of a non-defective via 120 to be inspected before cleaning,wherein upper peaks 150 represent the fluorescent signal received fromwalls 152 of via 120 (FIG. 10), and lower valley 154 represents thefluorescent signal received from pad 124. It is noted that lower valley154 has a small but measurable value due to the presence of a thinlaminate layer 122 which has not been cleaned out of via 120.

[0138] By appropriately pre-setting a lower threshold 158 and an upperthreshold 156, and ignoring the reflectance channel, processor 28 canapply lower threshold 158 to correctly identify the circumferenceboundary of via 120, similarly to reflective channel 32 (FIG. 3) andapply the upper threshold 156 to interpret whether the fluorescencevalue of the laminate layer 122 at the bottom of pad 124 is within anacceptable range for such a via before cleaning, or whether otherdefects, such as underdrilled laminate, breaks or unacceptably thicklaminate are present.

[0139] Operation of the dual threshold is generally similar to andself-explanatory in view of FIGS. 4A-9C, wherein the values derived fromgraph A with reference to lower threshold 158 are used in place ofvalues shown in graphs R in FIGS. 4B, 5B, 6B, 7B, 8B and 9B, obtainedfrom light intensity reflective channel 32 with respect to threshold RT,in order to define the boundary of via 120. Thus, in the preferredembodiment used to inspect vias before cleaning, light intensityreflective channel signal 32 (FIG. 2) is replaced by a luminescencesignal which is evaluated with respect to a low threshold 158. Lightintensity luminescent channel 130 is analyzed with respect to upperthreshold 156 to identify defects and its operation is substantiallysimilar to operation of light intensity luminescent channel signal 30 asdescribed in FIGS. 3A-9C.

[0140] The use of the information from luminescent intensity channel130, and analysis with respect to two discreet thresholds, as opposed toanalyzing information from both a luminescent intensity channel 30 andreflective intensity channel 32, has another benefit, in that system 10becomes less sensitive or insensitive to bright spots at the bottom ofvia 120, which may result, for example, be an uneven coating or laminateresidue covering pad 124.

[0141] It is appreciated that when applying a double threshold toluminescent intensity channel 130, typically it is necessary to modelvias 120 and to filter the signal and adjust gain in order to ensurethat a non-defective via produces a signal having distinguishable upperpeaks 150 and intermediate lower valley 154 and to account fortolerances in the acceptable thickness of laminate residues 122 in thebottom of uncleaned via 120, namely residue thickness that do result ina defect. Preferably, lower threshold is situated at a level just belowa minimum acceptable lower valley 154, and upper threshold can besituated at a level intermediate of lower valley 154 and upper peaks 150depending on the desired sensitivity for detecting residue laminate ordebris remaining inside via 120.

[0142] It is appreciated that an inspection system 10 may be equippedwith circuitry to perform via inspection in accordance with either ofthe methods shown and described with reference to FIG. 3 and FIG. 11.Alternatively, inspection system 10 may be equipped with circuitry ableto perform via inspection in accordance with both of the methods shownand described with reference to FIG. 3 and FIG. 11, in which case aswitch is provided to enable a user to choose whether to inspect PCBsprior to or after cleaning.

[0143] Reference is now made to FIG. 13 which illustrates an automatedoptical inspection and PCB laser drilling system 160, constructed andoperative in accordance with a preferred embodiment of the presentinvention. Automated optical inspection and PCB laser drilling system160 preferably includes automated optical inspection system 10 which isused to inspect PCBs 161 as described hereinabove. In addition, system160 includes a drilling laser 162 that drills holes or vias 164 in PCBs161. Both system 10 and drilling laser 162 are in electricalcommunication with a controller 166. It is appreciated that drillinglaser may be part of an integrated unit including inspection system 10and controller 166, or may be an add-on or modular unit. Additionally,drilling laser may be operative to drill vias both before and afterinspection, or alternatively drilling laser may be dedicated to theredrilling of vias only after inspection by inspection system 10.

[0144] Preferably system 10 is operative to automatically opticallyinspect the complete electrical circuit on a surface of a PCB 161, andto detect vias 164 which are either not defective, defective andrepairable (for example underdrilled vias and vias having debris andresidues therein) and non-repairable vias (for example vias havingbreaks or whose pads are misregistered). The position of defective andrepairable vias 164 on PCB 161 is fed to controller 166, which instructsdrilling laser 162 to redrill these vias 158, preferably automatically.

[0145] In accordance with a preferred embodiment of the invention, if adefective and not-repairable via is detected, for example a via with abreak or a misregistered via, none of the vias 164 are redrilled, inorder to conserve time and drilling resources. Thus if a defective andnot repairable via is detected, the PCB 161 including such a defectiveand not repairable vias may be discarded or sent to a different,typically non automated, repair station at which the nature of thedefect can be further evaluated and repaired as desired.

[0146] A preferred laser for redrilling the vias is a CO₂ laser, becausesuch a laser will not drill into the lower metal layer, as mentionedhereinabove. Alternatively, inasmuch as manufacturing processes require,automated optical inspection and PCB laser drilling system 160 mayincorporate a YAG or other laser that drills through both copper andlaminate. When such a laser is used, a number of different thresholdsare preferably applied in order to ascertain the existence of adefective via and to further determine the depth of under drilledlaminates or residues remaining in via 120 (FIG. 10). Once the thicknessof a residue is determined, laser driller is operative to automaticallyapply an appropriate quantity of laser energy to remove the underdrilledlaminate or residue without destroying the pad 124 at the bottom of via120. It is noted that controller 166 may be the processor 28 describedhereinabove. It is further noted that it is possible to use the samelaser to inspect and to drill the vias. Automated optical inspection andPCB laser drilling system 160 thus efficiently and rapidly inspects anddrills vias or holes in PCBs.

[0147] It will be appreciated by persons skilled in the art that thepresent invention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of the features describedhereinabove as well as modifications and variations thereof which wouldoccur to a person of skill in the art upon reading the foregoingdescription and which are not in the prior art.

What is claimed is:
 1. An automated optical inspection systemcomprising: a source of electromagnetic radiation for delivering aradiation beam on an article to be inspected; a plurality of sensorsarranged with respect to said radiation beam for sensing a plurality ofradiation properties associated with said radiation beam impinging atleast at a zone of impingement on a substance found on the article to beinspected, said plurality of sensors including a luminescence sensor forsensing luminescence of the substance due to the beam impinging thereonand a reflectance sensor for sensing reflectance of the beam from thesubstance said sensors transmitting information signals based on theradiation properties sensed by said sensors; and a processor incommunication with said sensors operative to receive the informationsignals for a plurality of zones of impingement, to combine said signalsfrom the sensors and to analyze them, and to generate an outputindicating the presence of defects based on said analysis.
 2. The systemaccording to claim 1 and wherein said defects include defects that areautomatically repairable and defects that are not automaticallyrepairable.
 3. The system according to claim 1 wherein said luminescencesensor comprises a fluorescence sensor.
 4. The system according to claim2 wherein said luminescence sensor comprises a fluorescence sensor. 5.The system according to claim 1 and further comprising a PCB with a viaformed therein, said via having a depth, wherein said reflectance andluminescence sensors are positioned at an angle with respect to the via,such that said sensors can view and provide sensed information generallyalong the entire depth of said via.
 6. The system according to claim 1wherein said sensors have an adjustable sensitivity.
 7. The systemaccording to claim 6 wherein the sensitivity of each sensor isadjustable independently of the other.
 8. The system according to claim1 wherein a position of each sensor is adjustable independently of theother.
 9. The system according to claim 1 wherein said radiation beamcomprises a laser beam.
 10. The system according to claim 1 wherein saidprocessor comprises a filter to filter out a level of luminescence whichcould cause a false alarm.
 11. The system according to claim 1 whereinsaid processor comprises a filter to filter out a level of reflectancewhich could cause a false alarm.
 12. The system according to claim 1wherein said processor processes said information signals into binarysignals with reference to predetermined detection thresholds forluminescence and reflectance.
 13. The system according to claim 1wherein said processor generates a binary image for each of luminescenceand reflectance.
 14. The system according to claim 13 wherein saidprocessor multiplies said binary images together, and calculates acomposite luminescence and reflectance image.
 15. The system accordingto claim 14 wherein said processor compares said composite image topredetermined defect parameters, and produces a defect report.
 16. Thesystem according to claim 1 and further comprising a drilling laseroperative to drill a hole or via in a PCB, said automated opticalinspection system and said drilling laser being in electricalcommunication with a controller, wherein a position of the hole or viais fed from said automated optical inspection system to said controller,which instructs said drilling laser to drill the hole or via.
 17. Thesystem according to claim 16 and wherein the position of the hole or viais fed from said automated optical inspection device if said hole or viais analyzed by the processor to be defective and repairable.
 18. Thesystem according to claim 16 and wherein said drilling laser isoperative to avoid drilling any holes or vias on said PCB if any saidhole or via is determined by said automated optical inspection system tobe defective and not repairable.
 19. The system according to claim 16wherein said drilling laser comprises a CO₂ laser.
 20. The systemaccording to claim 16 wherein said controller is said processor.
 21. Thesystem according to claim 19 wherein said controller is said processor.22. The system according to claim 16 wherein said drilling laser is saidsource of electromagnetic radiation for delivering a radiation beam onan article to be inspected.
 23. An automated optical inspection systemcomprising: a source of electromagnetic radiation for delivering aradiation beam on an article to be inspected; a sensor arranged withrespect to said radiation beam for sensing a radiation propertyassociated with said radiation beam impinging at least at a zone ofimpingement on a substance found on the article to be inspected, saidsensor transmitting information signals based on the radiationproperties sensed by said sensor; and a processor in communication withsaid sensor and operative to: receive the information signals for aplurality of zones of impingement, extract from the information signaladditional information about said article by analysis of the informationsignals with reference to at least two different thresholds, andgenerate an output indicating the presence of a defects based onanalysis of the extracted information.
 24. The system according to claim23 and wherein the processor further comprises an information combineroperative to combine the additional information about said articleobtained by analysis of the information signals with reference to atleast two different thresholds.
 25. The system according to claim 23 andwherein said defects include defects that are classified asautomatically repairable and defects that classified as notautomatically repairable.
 26. The system according to claim 24 andwherein said defects include defects that are classified asautomatically repairable and defects that classified as notautomatically repairable.
 27. The system according to claim 23 andwherein the sensor is a luminescence sensor operative to sensefluorescence.
 28. The system according to claim 23 and furthercomprising a PCB with a via formed therein, said via having a depth,wherein said luminescence sensors is positioned at an angle with respectto the via, such that said sensor can view and provide sensedinformation generally along the entire depth of said via.
 29. The systemaccording to claim 23 and wherein said sensor has an adjustablesensitivity.
 30. The system according to claim 23 and wherein saidradiation beam comprises a laser beam.
 31. The system according to claim23 and wherein said processor comprises a filter to filter out a levelof luminescence which could cause a false alarm.
 32. The systemaccording to claim 23 and wherein said processor processes saidinformation signals to produce a set of binary images with reference toat least two different predetermined detection thresholds forluminescence.
 33. The system according to claim 32 wherein saidprocessor multiplies said binary images together, and calculates acomposite image.
 34. The system according to claim 33 wherein saidprocessor compares said composite image to predetermined defectparameters, and produces a defect report.
 35. The system according toclaim 23 and further comprising a drilling laser operative to drill ahole or via in a PCB, said automated optical inspection system and saiddrilling laser being in electrical communication with a controller,wherein a position of the hole or via is fed from said automated opticalinspection system to said controller, which instructs said drillinglaser to drill the hole or via.
 36. The system according to claim 35 andwherein the position of the hole or via is fed from said automatedoptical inspection device if said hole or via is analyzed by theprocessor to be defective and repairable.
 37. The system according toclaim 35 and wherein said drilling laser is operative to avoid drillingany holes or vias on said PCB if any said hole or via on said PCB isdetermined by said automated optical inspection system to be defectiveand not repairable.
 38. The system according to claim 35 wherein saiddrilling laser comprises a CO₂ laser.
 39. The system according to claim35 wherein said controller is said processor.
 40. The system accordingto claim 38 wherein said controller is said processor.
 41. The systemaccording to claim 35 wherein said drilling laser is said source ofelectromagnetic radiation for delivering a radiation beam on an articleto be inspected.
 42. A system for repairing defective laser drilledholes in an electrical circuit to be inspected comprising: an automatedoptical inspection subsystem operative to inspect a PCB and to provideoutput indications of defective and non-defective vias on the said PCB,and a controller in communication with said automated optical inspectionsystem and with a laser drill, said controller being operative toinstruct the laser drill to automatically redrill at least some holes onthe PCB indicated as being defective.
 43. A system according to claim 42wherein the automated optical inspection system provides an output ofrepairable and not-repairable defective holes, and said laser drillautomatically drills defective and repairable holes.
 44. A systemaccording to claim 42 and wherein said laser drill avoids drilling anyholes if said automated optical inspection system detects a defectiveand non-repairable hole.
 45. A system according to claim 43 and whereinsaid laser drill avoids drilling any holes if said automated opticalinspection system detects a defective and non-repairable hole.
 46. Asystem according to claim 42 and wherein said laser drill is a CO₂ laserdrill.
 47. A system according to claim 42 and wherein said laser is aYAG laser drill.
 48. A system according to claim 47 and wherein theautomated optical inspection system is operative to determine acharacteristic of a repairable defective holes.
 49. A system accordingto claim 48 and wherein the characteristic of a repairable defectivehole is a size of an artifact in the hole.
 50. A system according toclaim 48 and wherein the characteristic of a repairable defective holeis a thickness of a residue laminate in the hole.
 51. A system accordingto claim 49 and wherein the laser is operative to provide an amount ofenergy that is adapted to clear the hole without overdrilling the hole.52. A system according to claim 50 and wherein the laser is operative toprovide an amount of energy that is adapted to clear the hole withoutoverdrilling the hole.